The present invention relates to compressed video data processing, and more particularly to a method for splicing MPEG-2 transport streams based upon locally available data.
In order to transmit data over limited bandwidth media it is often necessary to compress the video data signal to reduce its bandwidth. One of the video compression standards is the ISO/IEC 11172-2 MPEG-2 standard. Under this standard, frames or pictures represented by the video data signal are compressed as groups of pictures (GOPs), with the initial picture compressed as an I-frame, i.e., an internally compressed frame, and the others as P- or B- frames, i.e., predicted or bidirectionally predicted based upon the motion of the image from picture to picture. One of the problems with compressed video with motion compensation, such as MPEG-2, is that of switching between video data streams, or splicing two video data streams in sequence. Switching at an arbitrary point in an MPEG-2 data stream could result in switching between predictive frames in the two data streams with the result that there is an interval during which the picture is garbled since the predictive frames are no longer associated with the proper anchor, or I-frames.
What is desired is a method of splicing video in MPEG-2 transport streams that provides a smooth transition from one vide stream to the other.
Accordingly the present invention provides a method for splicing video in MPEG-2 transport streams based on locally available data, without depending on splice countdowns, closed GOPs or other splice-related information provided by upstream equipment. A first splice point is identified in a first video stream at an anchor frame, and a second splice point subsequent in time is identified in a second video stream at an anchor frame, the difference in time between the splice points forming a time span. A drain frame sequence is inserted into the time span to nearly empty buffers in a decoder. The drain frame sequence may be a black group of pictures (GOP) that is as long as necessary to fill the time span, or an extension of the last GOP of the first video stream in the form of freeze frames.
The objects, advantages and other novel features of the present invention are apparent from the following detailed description when read in conjunction with the appended claims and attached drawing.